Need help with passenger car lighting

[BruceG]

I'm using Rapido's Easy-Peasy lighting modules in some of my MTL heavyweights.  I'd like to add a rear marker light to the observation car using a 3V mini LED.  Since the E-P's use two 1.44 volt batteries, I thought I could use the module to power the LED as well.  However, touching the leads to the battery terminals, or one to a battery terminal and the other to the solder point for the reed switch produces no light.  Of course, I've tried switching the leads in all possible combinations.  Can anyone suggest what I'm missing about the lighting units?

Thanks,

Bruce

[craigolio1]

It could be that those batteries are wired in parallel, which would produce 1.5 V but with higher current capacity.  You would need an LED with a lower voltage drop.

When you are putting the leads of your LED in various places, do the remaining LEDs stay lit with same intensity? Get dimmer? Go out entirely?

Craig

[mmagliaro]

1. Put a voltmeter to the places you are touching your LED leads to, and tell us what voltages you are getting.

2. Never hook an LED straight across a voltage source with no dropping resistor in series with it.  I don't care what the expected battery voltage is or what the LED's forward voltage drop is.  Not having a resistor in there to limit the current is a recipe for instantly burning out the LED.  Are you sure the LED you are testing still actually works, since you were touching it to those batteries?  It may have fried instantly when you connected it across 3v is you didn't use a resistor.  I'd check that first.   Touch the LED with an inline resistor of 1k ohm or so to a 9v battery and make sure it lights

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I use the Easy Peasy strips myself.  Beware of a few things.  As-built, they only have about a 4-hour battery life.  That can be a real nuisance and adding another LED to the circuit will only shorten the battery life even more.  I found that since the car lighting is too bright anyway, I could insert a tiny 1/8w resistor into the Easy Peasy board to reduce the brightness (and the current draw), and bump the battery life up to more like 30-40 hours.  Also, use SR41 batteries instead of LR41.  The SR41 silver oxide have a much longer life.

Details:
LR41  capacity 32 mAh maximum
SR41 45 mAh

As it turns out, if you are game you can unsolder the tabs on the battery holders and bend the holders WIDER (NOT higher), and then resolder the tabs so that they can accomodate a wider SR45 battery, which is the same height as the SR41.  The batteries will still not stick out past the edges of the board, so the board will still fit anywhere it used to.
SR45 battery capacity is somewhere around 60 mAh, so it's about a 30% jump from the SR41.

[BruceG]

I did have a resistor on the LED. I also tested it afterward on a known power source, and it still works.  I don’t have a voltage meter, but can use one at our club this weekend.  That the batteries are in parallel is a good possibility. Their orientation on the board appears to make that likely.

Thanks for all the input!

Bruce

[glakedylan]

wouldn't installing 1 battery upside down (in reference to the other battery) make a series connection changing it from parallel?
just thinking out loud 

[Paradise275]

mmagliaro, can you show us where you insert the resistor. I find the lights too bright as well.

Rick

[mmagliaro]

wouldn't installing 1 battery upside down (in reference to the other battery) make a series connection changing it from parallel?
just thinking out loud 

If the battery holders are arranged in parallel, putting one battery in upside down will create a dead short and burn up both batteries in very short order.  You would be connecting one battery's "+" to the opposite battery's "-" and vice versa, exactly like cross-connecting jumper cables between car batteries, and... BOOM.

[mmagliaro]

I had an Easy Peasy lying around.

1. Batteries are in series.  Output voltage is about 2.8v total
2. Connecting an LED with 220 ohm resistor in series across the "+" and "-" solder pads at the end of the board
definitely works, and the new LED switches on and off with the magnetic reed, as you would expect.

Here is the extra LED installed and operating.





And here's a photo of where to cut a trace and solder in a resistor to dim the lights.  The resistor value will be up to you.
If they are still too bright for you, try a 330 ohm, for example.  If they are too dim, maybe an 82 ohm would be more to your liking.    I also replaced the LEDs with warm whites because the greenish ones that come with the board are just too darn "GREEN" for my taste, even if they are prototypical.

[Paradise275]

Thanks Max.
As always, the Railewire Guys are very helpful.

Rick

[BruceG]

Max, it appears that you have the older version of the lighting bar.  Rapido's new version has 6 small LED's arranged along the length of the board.  Much better car lighting effect but, alas, no solder pads that I can find.  Thoughts? [ Guests cannot view attachments ]

[Ed Kapuscinski]

Hey @rapidotrains.... on the next revision... solder pads!!

[mmagliaro]

Unfortunately, no, I don't have one of that newer revision.  And from those photos, I cannot make out the PCB traces, so I don't think I can help you from that.

Are the board traces clearly visible when you look at the board?  (I mean, is it just the photo that makes them hard to see, or is the board really painted over with some sort of black or dark brown paint, making the traces actually hard to see?)  If I could see all the traces clearly in a photo, I might be able to help you.

As for solder "pads", that's not really a big deal.  I only used the pads on my version of the board because they were conveniently exposed, tinned points into the switched output of the circuit.  I could have just scratched some lacquer off the traces at convenient points and soldered to them, which is what you'll have to do with the new board, I think.

[BruceG]

The traces are visible, but just barely.  I’ll try to photograph them tomorrow under soft daylight. Any artificial light I try is too harsh to allow the traces to show up.
Thanks for your help.

Bruce

[BruceG]

Max. . . How’s this? [ Guests cannot view attachments ]

[mmagliaro]

That is better, but it's still hard to really see where all the traces are.  I gave it my best shot, see below.

It looks to me like they have 3 resistors, each of which feeds a pair of LEDs that are in parallel.   "u1" is probably the flip flop that latches the circuit on or off when the reed switch closes, and C1, I'm guessing, is to debounce the reed switch so that when you pass the wand over it and it opens and closes several times in rapid succession (as reed switches are wont to do ), it doesn't annoyingly turn the lights on/off/on/off.. etc, and leave them "off" when you wanted them "on", or vice versa.

It looks to me like the LEDs are indeed wired in pairs, where each pair are in parallel and then wired through one dropping resistor.  So you have r1, r2, r3 on the board, each of which drives two LEDs.  You can't tap into LED points, because then your new LED will draw more current, and two of the other LEDs will dim or even go out entirely.

Instead you need to add a 4th resistor near that bank of 3 they already have on there.  I indicated where you have to tap it in, but there may be an easier spot.  See if you can find a trace where one side of all three of those resistors are attached.  That's where you want to tap off with a 4th resistor.  The place I indicated on the photo is just the tiny solder point where one of the resistors is soldered.  That will work, but you might not want to try soldering a very fine wire lead there, right where that surface-mount resistor is soldered, because that will be trickier than average soldering.

Once you have one end of the new resistor attached there, it goes to the LED, and then the other side of the LED can just go to any convenient spot along that long common trace that seems to go to all the LEDs.

Well... that's the best I can do from 10,000 feet up.  It's still kind of hard to see where the traces really go on that board from the photo.